This invention relates to linear electric motors and, more particularly, to a linear electric motor having a stationary winding and a moveable permanent magnet armature.
Recently the governments of many countries have imposed regulations on automotive manufacturers requiring that they meet progressively more stringent emission standards for and simultaneously reduce fuel consumption of automobiles. The manufacturers have encountered great difficulty in attempting to meet these two goals in an automobile of the size and performance desired by the market. To achieve a marketable automobile complying with current government regulations, all car manufacturers have concluded that they must provide a system of electronic control of engine performance. This system comprises a plurality of sensors for detecting performance parameters, a small computer for integrating the various performance parameters and specifying the necessary adjustments to be made to the engine to improve the performance parameters, and an actuator for effecting proper adjustment to the engine. One of the critical adjustments of an automobile engine is accurately adjusting the air/fuel ratio of the mixture of an engine carburetor by controlling the position of the carburetor metering rods. An actuator of the solenoid type is currently available for controlling the position of the metering jets of a carburetor and continuously retuning the carburetor several times per second. Retuning an engine carburetor several times per second by adjusting the air/fuel ratio of the mixture with a solenoid-type actuator has enabled automotive manufacturers to meet the current emission standards for and reduce fuel consumption of automobiles. It is, however, questionable whether the solenoid-type actuator can be employed for further effecting a decrease in engine emissions and/or decreasing fuel consumption, i.e., increasing engine efficiency. Accordingly, it would be desirable to provide an improved actuator for a carburetor of an automobile engine.
With current emphasis on gasoline conservation, national policy favors lowering of automobile fuel consumption. Improved metering of gasoline or fuel supplied by the carburetor of an automobile engine improves the air/fuel mixture and reduces unneeded burning of gasoline. To achieve the fastest response in any given system for a given force, acceleration of the moving member is maximized by having the mass of the moving member minimized. The solenoid-type actuator currently employed in an engine carburetor comprises a plunger of magnetizable material positioned within and circumposed by a stationary winding of current-carrying wire. When the stationary winding is energized, a magnetic field is produced and exerts a force on the plunger, thereby causing axial acceleration of the plunger relative to the stationary winding in the direction of the coil winding. However, due to inductance in the stationary winding, maximum acceleration response of the plunger is not attained. As current increases in the stationary winding, a change in the magnetic field results and produces an opposing voltage across the winding which decreases the rate of increase of the current in reaching full value. Since inductance in the electrical circuit opposes the change of current, cancellation of inductance is essential to achieve optimum acceleration for a given mass. It would, therefore, also be desirable to provide an actuator that overcomes the undesirable effect of inductance produced by the stationary winding of a solenoid.
The reluctance of the magnetic path in a solenoid-type actuator varies with the plunger position and varies the force acting on the plunger. Further, when the reluctance is a minimum and the magnetic centers coincide, the force exerted on the plunger is zero. Since force produced on a solenoid plunger is proportional to the current input to the second order, i.e., F=kI.sup.2, acceleration response is non-linear. As a result it is difficult to position quickly and accurately the plunger of a solenoid-type actuator with respect to its support frame. Further, the axial direction of the force and movement of the plunger of a solenoid is always in the same direction regardless of the winding direction of the solenoid coil or the direction of the current in the coil. It would therefore be desirable to provide an actuator where the force can be exerted in either axial direction.
Accordingly, an object of the present invention is to provide a new and improved permanent magnet electric motor having a stationary winding for moving the magnet in either direction.
Another object of the present invention is to provide a linear motor having a stationary winding and a pair of pole pieces secured to a permanent magnet for directing flux through the winding and for axially supporting the magnet.
Still another object of the present invention is to provide a linear electric motor wherein inductance of the stationary winding is cancelled to maximize acceleration of the armature of the motor.
An additional object of the present invention is to provide a linear electrical motor with a combination bobbin and armature bearing member supporting a stationary winding and an armature.
Yet another object of the present invention is to provide a small linear motor employable in a carburetor chamber of an automobile engine which imposes strict limitations on reliability and mass.
Still a further object of the present invention is to provide a linear electric motor having a winding and an armature provided with a pole piece not only directing flux to the winding but also connecting the magnet to an actuator rod for controlling the metering jets of an automobile carburetor.
Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.
Briefly, the present invention relates to a linear electric motor comprising a frame of magnetizable material, an armature movably supported by the frame, the armature comprising a permanent magnet having a pair of magnetic poles and a pair of pole pieces of magnetizable material, the pole pieces being secured to the magnetic poles. A stationary winding is secured to the frame and circumposes the pole pieces of the armature, and a bearing member of non-magnetizable material interposed between the pole piece and the stationary winding supports the armature. In another embodiment of the invention, a pair of pole shoes is fixedly secured to the frame.